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Abstract

A combination of geologic, petrographic and chemical criteria is used to classify the Erier basement rocks into three suites namely, the metagabbro-diorite (MGD) suite, the tonalite-granodiorite (TG) suite and the alkali-feldspar granite suite. The MGD suite is tholeiitic to calc-alkaline, metaluminous, with high Zr/Y ratio but having low concentration of incompatible elements (Zr, Nb and Y). The suite was produced by partial melting of mantle wedge at an active continental margin. The TG suite is calc-alkaline to alkaline with a trondhjemitic affinity. It also exhibits metaluminous to slightly peraluminous composition. The granodiorite variety was formed by 60 % fractional crystallization of a tonalitic magma mostly of plagioclase and hornblende with small amount of biotite at a destructive plate margin. The alkali-feldspar granite suite is weakly peraluminous, late-tectonic A2- subtype granites. It resembles the alkali-feldspar granite associations in Saudi Arabia and the Kadaweb post-kinematic granite of the Red Sea Hills in the Sudan that had been produced by partial refusion of the volcanic-arc protolith.